Electronic-photonic devices, also known as optoelectronic devices, are a class of electronic devices that are capable of sourcing, controlling, and detecting light. Electronic-photonic devices include both electronic and photonic functions. In the semiconductor industry, photonic devices have various cutting-edge applications including communication within a chip, between chips of a computer board, and between computer boards. In response to more demanding communication bandwidth, energy consumption, and performance standards for electronic devices such as semiconductor devices, photonic devices, e.g., photonic crystals, optical waveguides, are increasingly being integrated with optical/electrical circuits to form a type of electronic-photonic device called an electronic-photonic integrated circuit. In the electronic-photonic integrated circuit, the elements that perform the pure optical functions, the pure electrical functions and the optoelectronic functions may be formed concurrently, on the same or different substrate, using a CMOS process flow. The current CMOS process flow includes a series of complex fabrication steps including deposition, masking, etching and doping.
One advantageous photonic device is a photonic crystal, a material and/or lattice of structures, e.g., an arrangement of a plurality of holes, with a periodic alteration in the index of refraction. Photonic crystals have holes that allow customization of unique properties for electromagnetic wave propagation. Similar to the bandgap energy in semiconductors, where carrier energies are blocked, photonic crystals can provide a photonic bandgap for electromagnetic waves, where the presence of particular wavelengths is blocked while other wavelengths are allowed to pass through. The blocked directions are the “photonic bandgaps” of the structure. If the photonic crystal does not allow light to propagate within a wavelength range for all polarizations and directions, it has a “complete photonic bandgap.” Photonic crystals include two-dimensional (2D) and three-dimensional (3D) photonic crystals. 2D photonic crystals have periodicity in two dimensions and are uniform in the third dimension. Although a 2D photonic crystal cannot have a complete bandgap, it can have a blocked gap that exists for all directions and polarizations of propagation precisely confined to a particular plane of periodicity. By contrast, in 3D photonic crystals, the dielectric lattice is periodic in three dimensions, forming a complete photonic bandgap.
Another particularly useful photonic device is an optical waveguide, i.e., an optical path, formed on a substrate. A typical optical waveguide structure includes an inner core and an outer cladding material. The inner core may be formed of a material with a greater refractive index (n) than the index of the outer cladding material. Wave guiding occurs upon internal reflection of electromagnetic waves at the interface between the higher refractive index inner core and the lower refractive index outer cladding material.
Management of the differences between the inner core refractive index and the outer cladding material refractive index is needed to maintain uninterrupted propagation of optical signals through the waveguide with minimal leakage of the optical signal. Materials with a refractive index matching the refractive index of the inner core; even if spaced from the inner core, can couple with the inner core and attract optical signals away from the waveguide through a process called evanescent coupling, disrupting the propagation of optical signals through the waveguide. In particular, electronic-photonic devices and other electronic devices with electronic and photonic functions having various optical and electrical structures integrated on the same or different substrates can be susceptible to this type of optical loss.
A photonic device that mitigates optical loss from optical coupling and can also function as a photonic crystal to achieve a photonic bandgap of a certain value would advance the performance and efficiency of electronic-photonic devices and other electronic devices, e.g., semiconductor devices.